What more can I say ? It's clear that the auto_explain feature, which is a logging process, can make perfectly fine transactions being rolled back. That makes no sense, the transaction should be committed before any logging event is triggered, for me it's a bug in the core of postgres. It has nothing to do with the plugin used.
It may be an undesired behavior, and I do sympathize with the position, but the current design is quite intentional and long-standing and is not going to be treated as a bug to be fixed immediately and back-patched.
A query you can execute should be incapable of failing if EXPLAIN for the same query is issued. If some interplay with oracle_fdw causes this fundamental assumption to be falsified then auto_explain, which works under that assumption, and oracle_fdw are incompatible and you will need to decide which one (possibly on a per-transaction basis) you wish to use.
